Safety razor blade



I March 22, 1932. E THOMPSON 1,850,902

SAFETY RAZOR BLADE Filed Nov. 27, 1929 Fig.- 1.

. NVENTURL MM M- Patented Mar. 22, 1932 RALPH E. THOMPSON, OF BROOKLINE,MASSACHUSETTS, ASSIGNOR T GILLETTE SAFETY RAZOR COMPANY, OF BOSTON,MASSACHUSETTS, A CORPORATION 015 DELA- WARE SAFETY RAZOR BIiADEApplication filed November 27, 1929. Serial No. 410,220.

This invention relates to safety razor blades of the thin, flexible typewhich are bent transversely and maintained in acondition of pronouncedcurvature when clamped in the holders in which they are used. Suchblades as heretofore constructed have been subject to an objectionableamount of breakage, and the-object of my invention is to provide a bladeof this type which will not 19 break or crack under the normalconditions of use.

More specifically, my invention is intended to overcome the danger ofblade breakage due to stresses of abnormal amount or concentration suchas may result from anincipient crack or other imperfection in the bladeitself, and is characterized by the provision of a slot which extendslengthwise of the blade behind its cutting edge and by hav- 20 ing itsend portions of softer temper than its cutting edge portion throughoutareas which include the ends of the slot but do not extend to thecutting edge itself. The slot is of such length that it has the effectof concentrating in the end portions the stresses set up in the bladewhen the latter is bent transversely, leaving the remainder of the bladelargely free from stress, while in the relatively soft end portions inwhich the stresses are concentrated the elastic limit of the steel is soincreased that the blade will yield and change its shape before it willbreak or crack under any stress to which it is likely to be subjected.

My invention is particularly intended and adapted for double-edgedflexible blades, in which case the blade is preferably provided with asingle slotlocated midway between its 40 cutting edges Two embodimentsof my invention which have been selected for purposes of illustra-' tionare shown in the accompanying drawings, whereof, Fig. 1 is a plan viewon an enlarged scale of one form of double edged blade embody-,

ing my invention, and I Fig. 2 1s a similar view showing another form ofblade.

The preferred form of my blade, shownin Fig. 1, has two opposite cuttingedges 10, a central longitudinal slot 12 of substantially the samelength as the edges 10, squared end portions 14, and inwardly extendingrecesses 16 each located at one corner of the blade and forming the endboundaries of the cuttin edges and the side boundaries of the squaredend portions 14.

When a blade thus shaped is bent transversely the stresses developed areconcentrated mainly about the ends of the slot 12 and the inner anglesof the recesses 16, where the curvature is the sharpest and where inconsequence a crack is most likely to start. Accordingly Iprovide theends of the blade with relatively soft areas within which these pointsof concentrated stress are located and which preferably includetheentire end portions of the blade, being bounded by lines extending fromthe sides of the slot 12 near its ends to those portions of the recesses16 which form theend boundaries of the cutting edges 10, as indicated bythe dotted lines 20. I have found that it is possible to reduce, in theareas'thus defined, the degree of hardness to a point which willeffectively overcome any danger of starting a crack within the endportions of the blade while still preserving a degree of elasticitywhich will prevent the blade from taking an appreciable set when bent inits holder, butthe end portions may be made still softer if desired.When the each corner portion of the blade with a clear- 151 will ofcourse depend upon the composition ance space adapted to receive thecorrending corner of the blade-clamping cap,

i deformed, as explained in my nor application filed April 25 "19,29,Serial 0. 358,114. The. treatment of my blade necessary to produce therelatively hard and soft portions of the steel of which the blade ismade. In

the case of a blade made of carbon steel, which is the material commonlyused, I prefer to give the entire blade a suitable cutting edge temperthroughout and then soften the end I portions to the desired extent byconfining between cold clamps those portions of the blade which are notto be softened and subjecting the ex osed end ortions to heat. When thisproce ure is fol owed the cold clamps rotect the cutting edge portionsof the b ade from the direct action ofjthe heat employed to soften theend portions and also absorb the small amount of heat transmitted-by conduction from the endportions while being heated, so that the temper ofthe cutting edges and the blade material behind them is not materiallyaifected. In .the illustrated blade the softened area is substantiallyfan shaped but the exact shape of this area is of secondary importanceso long as it substantially includes the portions of the blade mostsubject to stress.

In the form of blade shown in Fig. 2, the end portions 34 of the bladeare rounded outwardly in the central portion and the cutting edges 30are somewhat shorter than the slot 32. In this case the stressesdeveloped when the blade is bent are not so concentrated at theperiphery of the blade as in the blade sh own in Fig. 1, so that theinner boundaries of the softened portions, indicated by the lines 40,may be considerably varied in position, provided that they lead from thesides of the slot to the periphery of the blade at points beyond theends of its cutting edges.

The rounded end portions of the blade shown in Fig. 2 may be soproportioned that if the blade is used in a Gillette razor a clearancespace will be provided beneath each corner'of the blade-clamping cap forthe purpose and with the result above explained, and it is an importantfeature of both of the forms of blade illustrated that the employment ofa slot which is substantially as long as the cutting edge makes itpracticable to combine the relatively soft and hard areas in the sameblade without causing the blade to warp or buckle, inasmuch as thecutting edge portions are substantially isolated from each gtihsr andfrom theremaining areas of the The apertures shown at 18 and 19 inFig. 1and at 38 and 39 in Fig. 2 are for the reception of the fpositioningstuds and center pin commonly ound in safety razors which. use flexibledouble-edged blades, but it will be understood that these apertures arenot es-' Having thus escribed my invention what I I claim as new anddesire to secure by Letters Patent of the United States is 1. A flexiblerazor blade adapted to be bent transversely when clamped in its holderand having two longitudinal cutting edges and a longitudinal slotlocated midway between them and having a length at least substantiallyas long as said ed es, whereb the stresses developed by bendlng the blae are concentrated in its end' ortions, the blade being provided at saiden portions with relatively soft areas which include the areas ofconcentrated stress at both sides of the slot substantiall as described.

2. A flexi le razor blade adapted to be bent transversely when clampedin its holder and having two longitudinalcnttin edges, a longitudinalslot substantially as ong as said edges and located midway between them,and

inwardly extending recesses located respectively at the corner portionsof the blade and forming the end boundaries of the cutting edges, thematerial of the blade being relatively soft throughout areas whichinclude the inner angles of the recesses and the ends of the slot butterminate within the cutting edge portion.

3. A flexible razor blade adapted to be bent transversely'when clampedin its holder and having two longitudinal cutting edges, a longitudinalslot substantially aslong as said edges and located midway between them,and inwardly extending recesses located at the ends of the cutting edgesrespectively, the blade being provided at its end portions withrelatively soft fan-shaped areas extending from the sides of the slotnear its ends to those sides of the recesses which formthe endboundaries of the cutting edges.

4. A flexible razor blade adapted to be bent transversely when clampedin its holder, said blade having a longitudinal cutting edge and alongitudinal slot located behind its cutting edge and at leastsubstantially as long as said edge, whereby the stresses developed bybending the blade are concentratedin the end portions thereof, said endportions being provided with relatively soft'areas which include theareas of concentrated stress substantially as described.

5. A flexible razor blade, resilient as a whole and adapted to bemaintained in a position of pronounced curvature when clamped in itsholder, said blade having a longitudinal cutting edge and a longitudinalslot substantially coextensive in length with said cutting edge andserving to concentrate in areas be on the cutting edge portions of theblade 1: e temgorary stresses due to bending, said areas 0 concentratedstress being resilient but relatively softer than the unstressed ortionsof the blade.

I Signe at Boston, Massachusetts, this twenty-sixth day of November,1929.

RALPH E. THOMPSON.

